My three year old son has been off Singulair for @4 weeks now. He...

You need to give him time and patience! Its rough. I feel it takes more than 4 weeks to come out of system. You also have to UNLEARN bad habits they have learned during this time. It is like now the cloud is lifted off their head they can now learn this behavior is not acceptable. Where before it didn't matter they were stuck in that zone and you couldn't break through to them. My son has been off since 3-29 and we have had dramatic improvements but he still tries to pull the tantrums here and there. The difference is it only lasts a short time compared to 2 hours or more and sometimes I can even talk him out of it alltogther. My son was on it for 3 1/2 years.