applying group working technique in grammar class

I applied this technique in my friend's class (K' Arbi) today to review the material (tenses) they have learned before.

I don't know what the appropriate name for this technique. Actually, I tried to combine some cooperative techniques tobe one new technique but the basic was group work.

PROCEDURE:

first, I divided the students into groups of four and five. Every group got one topic (e.g.: group one got simple present tense)
then, every people in a group will got a head number (A, B, C, D, & E)

Second, I gave them 15 minutes to discuss the topic.

third, every group presented the topic. because the topic about tenses, So, every group should give explanation about: the function of that tenses, the application of that tenses in the sentece, and conclude the pattern from the example of sentences they had made.
every student in group would have job in presentation. one student explain the function, another one explain the pattern, the others gave example. to determine who got what job, we use a lottery (their head number)

forth, other groups paid attention to the speaker and took a conclussion after one group present their topic. so, we can check their understanding. this step was guide by the teacher.