A musician wants to evaluate whether providing praise for offort versus providing praise for achievement might result in butter musical performance, She sglocis 60 kanth- grade classrooms using a random process, in half of the classrooms, the music teachers provide praise for high offord In the other half, music loachers provide praise for Leigh achievement. The number of children in each of the classrooms was the same IQ scores varied across classrooms Performance was measured by the overall grade each musician received at the end of the school year using a letter grading system (A B, C. D. or F) What is the control variable in this experiment? Number of children per classroom Type of school district Type of praise given Overall grade given