Can anyone give me advice on an 8 year old who is having problems with taking things seriously in school?

i don't agree with any child. there are other ways of dealing with bad behavior. so why have you not taken things away from him? some times kids will only respond when you take things they really like to do away from them. i think for the summer, you need to take any game systems away from him. make him sit down during the day and do some reading, writing, math. only when he does this would i allow him outside to play. let him know that he needs to improve in school. when school starts up again and he does well, then slowly give him things back. if he has a tv in his room you need to take it out. only allow him to watch tv in the living room with the rest of the family. you need to put your foot down. doing these things are not going to hurt him physically. like a would. also writing the same sentence over and over is foolish. he is not learning anything by that. as i said make him do some work in his reading writing and math each day.he is only 8 you can not keep him tied to the house all day. maybe explain to him that you know he can do well. so you going to do a give and take. if he does really well with this during the summer. let him know how proud you are and that you expect him to do well in school and take him out for a special treat. good luck.