Helping older students needs to appear as if you weren't there. They need to plan and execute everything from weekly homework and home reading to term projects and researched reports. After all, we want them to become independent workers and thinkers. After we set editing standards, we need to take a giant step back during the task itself so kids can solve as much as possible of their own problems. We can assist but should never do school work for our kids.
If they don't freely discuss their homework or projects, then ask questions: What is your homework tonight? Do you have questions I might be able to help you understand? When is the book report due? How long is the report to be? What are your goals on the project? (usually guidelines are sent home with projects)
Regardless of the task, it is important to also establish the role of editor early on as a way to help a child meet school standards and expectations. Edit the work while it is still in its rough form and easy for a child to make changes. Set unwavering expectations that all school work is to have the best written form, spellings, punctuation and grammar, unless it is a practice or review page and there is not that expectation.
Our best assistance also provides background support. Set up family standards and let kids know the adult's role: purchase the project materials, help locate resources and provide an audience for their practicing. We need to let students make as many decisions as possible, but the quality of their work should never be left to chance.