Your 7 year old is now gaining lot of confidence day by day. He would also be facing a lot of competition from their peers which sometimes make them frustrated trying to keep up with them. They tend to lose self-control and behave badly and thus you might have to step in to discipline them.
What you need to know
When you want them to do something, give them healthy choices – it could be some errand or homework or a household chore. Ensure the choices are to do it in order or as according to the priority but let the choice be theirs. That gives them a boost and helps to reduce their arguing since it would be their choice. If you find them facing any problems, together try to find solutions along the way making them realize why something went wrong and how it can be avoided and be done better the next time.
Since your kid is now able to understand with reasoning use logical consequences. This helps them to think twice before repeating any bad behaviour. Praising a child will never make them over-confident but gives them the lift required to meet your expectation. Recognize their effort and the perfection in their activities.