What should I do for my son?

He is 13 and has ADD,the inn-attentive type-he is not hyper at all.I have him in resource for two cles out of 7,he gets extra time on ignments,and is supposed to bring home a work contract daily to keep track of ignments.This past week however he has not brought the contract home-he says he forgot,or he lost it.He had a spelling packet that was due today-he told me he lost it,but his teacher emailed me and said he told her that I spilled soup on it and threw it away!!He lied to his teacher,which really makes me upset.I feel like I cannot trust him.Has anyone here dealt with this,and what did you do?I have tried taking away privileges,but it only works for a little while.I really hate this.