S.H.
After school is when I assume, you have him study?
That is what I do with my daughter.
I also have a son, her younger sibling.
They are 4 years apart and very close.
But, after-school, I always let my daughter unwind & deflate... have a snack and PLAY with her brother and he with her.
So they do get that time... together, after school and BEFORE she has to study.
At a certain time, on the clock, she knows it is homework/study time.
So... until then, as I said, I let her and her brother hangout/play and just have fun/relax.
And it works out.
Then when she is studying, my son KNOWS, he cannot make a lot of noise... but often, he is napping at that point.
So... I would, look at how you are sequencing the after-school routines....
For my daughter, homework is after-school, after deflate/relax/unwind time and with her brother. THEN... it is homework time. And homework time is always.... after-school, not after dinner. By then, it is too late, too rushed, she is too tired, and it is just not a good timing, for homework.
AND also though, you need to emphasize with the other kids, that it is 'quiet' time. So your son, can, study.
But you need to verbalize all of this to all your kids. The sequencing of things....
TELL your 1st grader... that he comes home, then can PLAY and deflate/have a snack after school. THEN at a certain time... it is homework time and with you. THEN his siblings have to go elsewhere and have 'quiet' time. And he has to study.
all the best,
Susan