Select representative pieces from across the year's writing and write a specific reflective introduction for each, showing growth.
A portfolio is a deliberately chosen set of your best or most meaningful writing from the year -- not everything you wrote, but a handful of pieces that together show real range and growth: the argument essay, the research report, the historical narrative, and the mini-research presentation.
Each portfolio piece needs a short reflective introduction, written now, with the benefit of looking back over the whole year. A strong introduction names a specific skill the piece demonstrates and, where honest, how that skill has grown since earlier in the year.
Mastery looks like: They select a varied, representative set of pieces and write specific reflective introductions naming real skills and growth.
Common stumbles: Writing a vague introduction ("I worked hard on this") instead of naming a specific skill or comparable moment of growth.