The best first step any educator or school should take is establishing an honor code. Cheating is sometimes the result of students not understanding what is and isn’t acceptable, and simply explaining what constitutes cheating (plagiarism in particular) can make a significant difference. Effective honor codes make clear that the work students submit must be their own, and they have completed it using the knowledge and skills they’ve acquired over time.
Additionally, setting real consequences for breaking the honor code is a good way to help students understand the severity of doing so. Consider creating a contract for students and families to sign that clearly lays out online learning expectations and consequences for not meeting them so everyone understands what students need to do to be successful in their coursework.