If you read this Forum on any regular basis, you will likely predict what I am going to say. When a child has been behaving well, then rather suddenly takes a protracted downturn, usually some changes in the environment are instrumental. So take a look at what changed between first and second grade, and this might help to locate the source of the stress. Now, regardless of external stressors, you've got to respond to the behavior. I'd guide you away from corporal punishment, simply because it has limited value. Instead, use a sytematic reward/punishment system that is organized in 24-hour blocks. Each day should start anew. If you haven't already done so, establish a daily reporting system (it needn't involve detailed information) from the school, so you always know how things have gone. Make privileges such as outdoor play, TV, video games, etc. contingent on following the rules - i.e., he 'earns' these privileges each day, depending on his performance. You might take a look at Lynn Clar's SOS: Help for Parents - it is a practical guide for the sort of behavior management I'm advocating.
Yes, it sounds like your step-son and my grandson have the same problem. My daughter has put him in ti-kwan-do and hopefully this will help. I have found out that he does not like his reading teacher, but likes his home room teacher. All the problems has happend in his reading class. He is a very good reader. I do know that the teacher put him in the back row so he does not disrupt the other students, he is not the only one back there, there are 2 other kids and 1 outside the class room. The teacher told my daughter that she puts the kids that are disruptive in the back and outside, for sitting in the front of the class was a privledge. When I was in school, sitting in the front was not a privledge, it was so the teacher could keep and eye on you. I feel the teacher has no control of her class. He does pretty good at home. He has come up with forgetting a lot. If he doesn't want to tell you something or bring his homework home etc. he says "I forgot".
Hoepfully we all can come up with what is bothering the boys', I don't know about your step son but this is just not like my grandson to be doing this, he has always been a pleaser and very loving.