State an opinion clearly using a phrase like "I think" or "In my opinion," and support it with one solid reason.
An opinion is what you believe, not something everyone would agree is true. Strong opinion writing often starts with a clear signal phrase like "I think" or "In my opinion," so the reader knows right away that a belief is coming.
A reason is real support for your opinion -- not just repeating it. "In my opinion, recess is the best part of the school day because it lets our brains rest" gives the reader a true reason to consider.
Mastery looks like: They open with a clear signal phrase, state an opinion, and support it with one real, specific reason.
Common stumbles: Writing a reason that just restates the opinion in slightly different words, such as "because it is great."