This report will show the influence of the size of the group and the teaching method on an intensive lasted attention paid by students and their motivation for students belonging a second class room level in physics and chemistry. Experimentation had been performed though pratical working sessions. The first run consisted in having the Zazzo barrage test passed in order to select students according their level of attention into three classes : high, medium and low. Two trials were carried out, one as a directed experimentation and the other one as a free experimentation based on investigation process. For each case students were either in groups of two or groups of four individuals. The analysis of results shown that the more free was the teaching activity the higher attention and the more motivated were the students. It also revealed the group of four was more beneficial toward lasting of attention and students were even more motivated.