suppose an experimental study randomly assigns 100 9 year olds to have a large nutritious breakfast each day, while another 100 are assigned a small nutritious meal each day. Academic performance among those with a large breakfast was on average, much better than the other group. Is this evidence that the parents should require their own 9 year olds to have a large nutritious breakfast? explain.

I said No, there are many other variables that are not considered like IQ, etc... and my teacher said shouldn't random assignment take care of this?

Is there something I'm missing here?

Question

suppose an experimental study randomly assigns 100 9 year olds to have a large nutritious breakfast each day, while another 100 are assigned a small nutritious meal each day. Academic performance among those with a large breakfast was on average, much better than the other group.  Is this evidence that the parents should require their own 9 year olds to have a large nutritious breakfast? explain.

I said No, there are many other variables that are not considered like IQ, etc... and my teacher said shouldn't random assignment take care of this? 

Is there something I'm missing here?