ABSTRACT
The analyses in kibbutz, middle school samples confirmed two of the three hypotheses: that classroom intellectual composition positively affects objective academic achievement, and that compositional effect is stronger among low resourced students. The third hypothesis, of the amplified effect in the middle range of the ability distribution, was confirmed in the kibbutz sample only. In the kibbutz sample a quasi-experimental comparison was made between two treatments: heterogeneous homeroom classes versus homogeneous classes of low and high ability levels. In the middle school sample the effect of a continuous treatment variable was examined: the intellectual composition as represented by the mean academic achievement in the class. Though fairly heterogeneous intellectually, the sample was highly homogeneous in student ethnic and socio-economic background. The relative weakness of the ethnic factor has important implications both for the implementation of educational integration in Israel and for the investigation of its scholastic outcomes.
