Focus on School w/ a 4 year old

Hello Everyone! Long time lurker, I really appreciate the advice that comes through here. I have a 4 year old son who is 95% awesome! Hes funny, he loves to talk, we play, he's engaged. However to schoolwork...its been a hellish battle.My ex-husband and I split custody and he is with him during the week and me on the weekend (I have 0 family, and he has his grandmother, grandfather, aunts, etc. and ex has a great school system). Recently I have noticed on my weekends, its been harder and harder to do anything "educational". I've always read to him before bed, sing songs, keep educational toys about (very little tablet time)...but he just has 0 interest in learning.As he just turned four he can count to 20 on his own, and we sing the alphabet together, and he knows shapes and colors, but he doesnt want to sit down and practice writing or his letter recognition at home or school. His daycare says we need to do focus exercises with him, as its the same at school...he wants to play and be a goofball 24/7. I talked to his Dad and he is extremely busy, I dont know he is trying to sit aside the 10-15 minutes a day I am to do a page in a workbook or lesson.I've recently bought some pre-school workbooks and bright colors and pencils, as well as spelling blocks. I try to sit down with him each day to practice but he honestly has 0 response.What can I do? I dont know if its a mental issue because he is a single child (we divorced when he was 1), and he has a lot of attention on him? Or could it be a focus issue (I struggled with ADHD when I was a child and still take medicine to this day to focus at work)...thoughts?Edit: I didnt want to make it sound like it was just workbook work. I actually sit down with him with big colorful crayons, large pads, and we do it together. We do activities to run and touch colors of the letters and then trace (however I have not been using alternative "inks") Its just been concerning when I give him the pen to try he just draws all over the page, refuses to trace, etc. Anything educationally focused, on paper, he just tunes out. We count when we bake together, we count when we read, just when I show him the actual number in print he just zones. :( via /r/Parenting http://ift.tt/2iNE4tI