Select representative pieces from across the year's writing units and write a brief rationale explaining what each piece demonstrates.
Portfolio curation is its own form of analysis: looking back across a whole year of writing -- the argument essay, the medieval research report, the historical-fiction story, the literary analysis -- and choosing which pieces best represent real growth and genuine skill, not just which pieces were easiest or most fun to write.
Each chosen piece needs a brief rationale: a sentence or two naming the SPECIFIC skill or growth that piece demonstrates, not "I liked this one" but "this piece shows I can integrate evidence smoothly" or "this shows real progress revising for cohesion" -- exactly the kind of specific, evidence-based thinking practiced all year in analysis writing.
Mastery looks like: They select three or four representative pieces from across the year's units and write a specific, skill-focused rationale for each choice.
Common stumbles: Choosing pieces based only on enjoyment rather than demonstrated skill; writing a vague rationale that could apply to any piece rather than naming something specific.