The Law Commission says the Ministry of Education has little power to take action against private schools, even if the welfare of students is at risk.
The commission has reviewed private school regulations and says they don't give the ministry sufficient powers if it has concerns about a private establishment.
It says the ministry feels unable to act in some circumstances or chooses not to because of uncertainty about the extent of its powers.
The review followed complaints led by Green MP Sue Bradford that some private Christian schools could get away with using corporal punishment.
The Ministry of Education declined to comment.