The purpose of this study has been to find outrnthe effects of ability grouping on the instructionalrnprocesses , that is, on the uti lization of resources,rnapplication of the different methods and techniques ofrnteaching , the academic achievement; the socials and emo tionalrndevelopment of the students; and final l y, its effects on thernworking cond i t i ons and work relationship of the teachingrnstaff in selected senior secondary schools of Addis Ababa.rnTo this end, samples of students and members of thernacademic staff have been selected random l y and were made tornfill in the questionnaires prepared for each of them. Inrnaddition to this, a randomly selected the Ethiopi ~Sc h oo lsrnLeav ing Cert if icate Examination ( ESLCE ) results of a matchingrnhe terogeneously taught students and a homogeneously treatedrng r oups; a randomly selected c l assroom observations andrninterviews with the regional education office authoritiesrnhave been used as the sources of data.rnThe analysis o f the data col l ected fr om the d ifferentrnsources s h owed that there are no significant differences inrnthe utilization of the resources o f the schoo l s , in thernapplication of the different methods and techniques ofrnteaching. Similarly, the comparison of the academicrnachiev ements of t he heterogeneously taug.t students of thepre -g r ouping ability prac tice and those o f the homogeneouslyrngrouped and taught students haven 't shown significantrndifferences which are in favour o f the special grouping.rnThus. showing that the expected purpose s o f the groupingrnpractice in the region have not been attained.rnAlthough the re are no significant differences in thernAcademic ach ievements. the grouping practice has showed somernpositive and negative effects on the social and e motionalrndevelopment of both special and non-special group student.rnHowever . the negative effects seem to be more and stron/j[er onrnthe non-special group students.rnThough there are the des ire to exce 1. highrninte llectua l curiosity, self-reliance.rnsociability and truthfulness among thernindependence.rnspec ial c lassrnstudents. t here are some negat i ve c haracte ristics that arernman ifested by them. These inc l ude. the artif i cially inflatedrnself-esteem or superio rity corrlPelex. boasting. and somernothers which have not been o bserved in the heterogeneo u s l yrngrouped students by the staff and the students the mselves .rnThe negative effects o f the prac tices seem to bernhigher and stronger on the non-special class students than onrnthe special c l ass stude nts. It has stigmatized t hem . Itrnmade them feel inferior to their pee rs . lose interest in thernschool. develop low self-image. lac k self-contro l . etc.Finally, the findings showed that the abilityrngrouping practice has not showed any significant effect onrnthe teachers' working conditions and work relationships.rnThis is so, because there have been no clearly statedrnguidelines as to how the practice has to be accomplished andrnthe demands and competenc i es required from the teaching staffrnwhic h consquenty would have affected then!. They teach almostrnas wha t they had been doing in a heterogeneously groupedrnclasses . The teaching met hods and techniques they use in thernspecial and non- special classes are more or less the same .rnTherefore, the effects o f the practice on the teaching staffrnare lirr!ited.rnEventhough the contribut i on o f the ability groupingrnin the schools a re very limited, its negative effects on thernstudents are higher than its pos itive effects. To maximizernthe contribution of t he p r actice i n the instructiona l p r ocessrnand minimize t.he negat i ve effec ts, it needs a c l early setrnguidelines on the different activities. The teachers needrntraining. The separation o f the school who lly f o r thernspecial students seems logical. In addition t o this, thernnumber of sections and the large size of the students in eachrnsec tions are Borne o f the great obstacles to mate rialize thernplan. So it needs great attention to get good results fromrnthe practice .