JUSTICE STEIGMANN delivered the opinion of the court:

Plaintiffs Ruth Peacock, Pierce Farms, Inc. (PierceFarms), Stephen Acres, Inc. (Stephen Acres), Courtney Stephens,Margaret Stephens, Raymond Lippert, and General Bank Trust(General Bank) appealed their property tax assessments to theIllinois Property Tax Appeal Board (Board). The Board consolidated plaintiffs' appeals for hearing purposes. In July 1998,the Board granted partial relief to Stephen Acres and GeneralBank but otherwise denied plaintiffs' appeals.

Later in July 1998, plaintiffs filed a complaint in thecircuit court, seeking administrative review of the Board'sdecision, and in addition to the Board, named as defendants thefollowing parties: Max Coffey, as Chairman of the Board; theCounty of Adams, in and for the State of Illinois; the AdamsCounty Board of Review (Review Board); the Board of Education ofCommunity Unit School District No. 3, Adams County, Illinois; theBoard of Education of Community Unit School District No. 337,Counties of Hancock, Adams, and Schuyler, Illinois; and the Boardof Education of Community Unit School District No. 4, Counties ofAdams and Hancock, Illinois.

In November 1999, the circuit court dismissed plaintiffs' complaint, pursuant to section 2-619 of the Code of CivilProcedure (Code) (735 ILCS 5/2-619 (West 1998)). Plaintiffsappealed, and this court reversed and remanded. Peacock v.Property Tax Appeal Board, No. 4-00-0162 (November 30, 2000)(unpublished order under Supreme Court Rule 23).

On remand, following hearings in March and June 2002,the circuit court reviewed the Board's decisions and affirmedthem.

Plaintiffs appeal, arguing that the circuit court'sjudgment was against the manifest weight of the evidence. Weaffirm in part, reverse in part, and remand with directions.

This consolidated case involves the following propertytax appeals: (1) Courtney and Margaret appealed the propertytaxes on their home in Golden (the Stephens home) for the years1987 through 1997; (2) Stephen Acres appealed the assessments forimprovements on its farm property (the Stephen Acres farm) forthe years 1987 through 1997; (3) Peacock appealed the propertytaxes on her home in Quincy (the Peacock home) for the years 1987through 1990; (4) Pierce Farms appealed the assessments forimprovements on its farm property (the Pierce farm) for the years1991 and 1992; (5) General Bank appealed the assessments forimprovements on its three properties (the Bank properties) forthe years 1986 through 1990; and (6) Lippert appealed the property taxes on the Bank properties for 1985, the year in which heowned them (collectively, the subject properties). Specifically,plaintiffs alleged that (1) their properties and improvementsthereon were not assessed at the same percentage proportion tofair cash value as other properties in Adams County; and (2) thefarm outbuildings on plaintiffs' properties were not assessed onthe basis of their current use contribution to the productivityof the farms, as is required under section 10-140 of the PropertyTax Code (35 ILCS 200/10-140 (West 1998)).

In May 1998, a Board hearing officer conducted ahearing on plaintiffs' consolidated cases. Because the partiesare familiar with the evidence presented at the May 1998 hearing,we review it only to the extent necessary to put plaintiffs'arguments in context.

William Cornwell testified that he had been a licensedreal estate broker since 1963 and was an experienced appraiser. Cornwell appraised all of the subject properties and the properties that he described as "comparables." The comparables hadbeen chosen by Courtney.

Evidence showed that Courtney used the comparables tocreate a document entitled "Appellants' Assessment Ratio Studies," which was admitted into evidence. Courtney's study coveredthe years 1985 through 1997 and included between 9 and 19comparables for each year. The study showed the fair marketvalue of the comparables for each year based on either Cornwell'sappraisals or a recent sale of the property if one was available. The study also showed the assessed valuations for each of thecomparables. Under a column titled "ratio," the study purportedto show the percentage of fair market value at which each property was assessed. The study also showed an average percentagefor all of the comparables.

Courtney testified as follows regarding how he chosethe comparables used in his study: "I just went through therecords of the assessor's office and chose them based on thefigures I found there." He acknowledged that he did not randomlyselect the comparables, but chose specific properties. Courtney's only criteria for selecting a property to be used as acomparable was that it had been assessed low. He did not consider whether the properties to be used as comparables weresimilar to the subject properties.

According to Courtney's study, the ratio of assessmentto estimated market value of the comparables for the relevanttime period averaged from 7.88% to 18.22%. For the same timeperiod, the ratio of assessment to estimated market value of thesubject properties ranged from 32.21% to 77.50%. (Pursuant tosection 9-145 of the Property Tax Code, property shall be assessed at 33 1/3% of its fair cash value. 35 ILCS 200/9-145(West 2000).)

Georgene Zimmerman testified that she had been theAdams County supervisor of assessments since 1990 and the deputysupervisor of assessments for many years before that. Zimmermancreated her own assessment ratio study by taking all "usablesales" that took place in the multi-township assessment districtof Houston and Northeast Townships and comparing the sales pricesto the properties' assessed values. "Usable sales" were thosethat were arm's length, and were not executor's deeds, quitclaimdeeds, splits, or farmland sales. Zimmerman summarized her datain a manner similar to that used by Courtney. Her chart includedsome of Courtney's comparables in addition to others; she usedall of the available sales for the given year. Zimmerman did notchoose only the highest sales.

Zimmerman further testified that on Courtney's 1997chart, in three instances, the sale price used was for a 1997sale of a residence, but the assessment for that year was for alot only. Thus, the numbers showed a low percentage ratioassessment. In a separate instance, the assessment did notreflect what was actually sold due to a split of existing parcels. In another instance, one of Courtney's comparables was a"10-30" assessment, which reflects an assessment rate temporarilygranted to a developer until a lot is sold or developed. Suchassessments are "special" and not based on fair market value.

Cornwell testified that he appraised the farm outbuildings on the subject properties by determining the value of theircontribution to farm productivity. He determined the value offarm buildings to farm productivity based on his experience andhis observations of the subject properties. He described hisrelevant experience as follows: He was raised on a farm and hadowned farms. After he went into the real estate business, heacquired and operated several farms that had farm outbuildings. Cornwell said he ascertained the value of the properties merelyby looking at them and deciding what they were worth based on hisexperience.

Dennis Grimm testified that he had been a licensed realestate broker in Illinois since 1976, and Quincy's deputy taxassessor since 1978. Grimm explained how he appraised the farmbuildings on the Stephen Acres farm as follows: "Well, havingnot a lot of experience in that sort of thing, what I did was Idrew on the experience of others that are in that business, localappraisers, once again, local [r]ealtors that are in the Goldenarea that are familiar with farming and that property." He alsotalked to local lenders that do a large amount of farm lending.

Grimm further testified that when he appraised the farmoutbuildings on the subject properties, he did so by determiningthe replacement cost of the building and subtracting appropriatedepreciation in accordance with the requirements of the IllinoisReal Property Appraisal Manual (Appraisal Manual). When askedwhether he valued the farm outbuildings based upon their currentuse and their contribution to the productivity of the farm, Grimmanswered, "I guess I did not."

Roy Points testified that he had been the Quincytownship assessor since 1990. From 1980 to 1990, he was theAdams County supervisor of assessments. Points acknowledged thatunder the law, farm outbuildings should be assessed pursuant toIllinois Department of Revenue guidelines, which state that suchbuildings should be assessed according to contributory value. The Appraisal Manual provides that farm outbuildings are to beassessed on a cost approach "with a determination based on howthey're used to reflect obsolescence, whether there's any functional obsolescence or not." Thus, the cost approach is only astarting point.

Points further acknowledged that the Board's information pamphlet provides as follows:

"Farm outbuildings are improvements on thefarm such as housing for animals or machineryand storage for feed and grain. These structures are assessed at 33 and a third percentof their contributory value to the productivity of the farm. Contributory value considers the current use of the improvements andwhat that use adds to the overall productivity of the farming operation. This part ofthe farm property assessment is subject onlyto county board of review factor."

The Board rejected plaintiffs' claims that theirproperties were unfairly assessed at a higher assessment tomarket value ratio than other properties in Adams County. In itswritten decisions on each of plaintiffs' appeals, the Boardaccorded little weight to Courtney's assessment to market valueratio study because (1) the study used Cornwell's appraisals,which were based solely on his experience and not supported bycomparable sales or market value documentation; and (2) Courtneytestified that he selected the comparables based on their lowassessments.

As to plaintiffs' claims that farm outbuildings had notbeen properly assessed, the Board granted partial relief toStephen Acres and General Bank, upon determining that some oftheir properties had been overvalued. Specifically, the Boarddetermined that (1) Stephen Acres was entitled to a reduction forfarm improvements for the 1989 assessment year; (2) General Bankwas entitled to reductions on a parcel including a residence andfarm improvements for the years 1985 and 1986; and (3) GeneralBank was entitled to reductions on another parcel, including farmoutbuildings for the years 1988 through 1990.

In July 1998, plaintiffs filed a complaint in thecircuit court, seeking administrative review of the Board'sdecisions, and the court dismissed plaintiffs' complaint. Plaintiffs appealed, arguing in pertinent part that (1) theAdministrative Review Law (735 ILCS 5/3-101 through 3-113 (West1998)) does not require plaintiffs to request issuance of asummons to each defendant; and (2) their failure to cause summonsto issue to each defendant should be excused because they made agood-faith effort to comply with the relevant provisions of theAdministrative Review Law. This court agreed with plaintiffs andreversed. Peacock v. Property Tax Appeal Board, No. 4-00-0162(November 30, 2000) (unpublished order under Supreme Court Rule23). Following remand, the court conducted hearings on plaintiffs' complaint, and in a March 22, 2002, written order, thecourt affirmed the Board's decisions. Specifically, the courtfound that the Board's acceptance of the evidence presented bythe Review Board over plaintiffs' expert testimony was neithercontrary to statutory requirements nor against the manifestweight of the evidence. This appeal followed.

As a threshold matter, we first address defendantschool districts' argument that both the circuit court and thiscourt lack jurisdiction over them because following this court'sNovember 2000 remand, they were not properly served with asummons. We disagree.

This issue was addressed at some length in the firstappeal of this case. Peacock v. Property Tax Appeal Board, No.4-00-0162 (November 30, 2000) (unpublished order under SupremeCourt Rule 23). In our November 2000 order, we rejected theschool districts' arguments and held that (1) plaintiffs hadcomplied with the requirements of section 3-105 of the Administrative Review Law (735 ILCS 5/3-105 (West 1998)); and (2) thecircuit court should not have dismissed plaintiffs' complaint. Our order did not require that plaintiffs take any further actionon remand, and we adhere to that decision.

We further reject the school districts' remainingarguments regarding personal jurisdiction. As of November 17,1999, all defendants had made general appearances in the circuitcourt and thus cannot now challenge the court's jurisdiction. See In re Possession & Control of the Commissioner of Banks &Real Estate of Independent Trust Corp., 327 Ill. App. 3d 441,464, 764 N.E.2d 66, 87 (2001) ("If a party participates in theproceeding on its merits, even after a special appearance hasbeen filed, that party waives the special appearance and jurisdictional challenge when he takes such affirmative action dealingwith substantive issues thereby amounting to a general appearanceand submitting himself to the jurisdiction of the court").

Appeals from the Board are governed by the Administrative Review Law. 35 ILCS 200/16-195 (West 2000). Under theAdministrative Review Law, we review the administrative agency'sdecision and not the circuit court's determination. XL DisposalCorp. v. Zehnder, 304 Ill. App. 3d 202, 207, 709 N.E.2d 293, 297(1999). When conducting such review, we accept the administrative agency's findings and conclusions on questions of fact asprima facie true and correct. Our review is limited to determining whether the agency's findings are against the manifest weightof the evidence, which means that "all reasonable and unbiasedpersons would agree that the opposite conclusion is clearlyevident." National City Bank of Michigan/Illinois v. PropertyTax Appeal Board, 331 Ill. App. 3d 1038, 1042, 780 N.E.2d 691,695 (2002).

Section 1910 of Title 86 of the Illinois AdministrativeCode (Administrative Code) governs the practice and procedure forhearings before the Board. 86 Ill. Adm. Code