Here are my posts that focus on teaching Spanish to heritage speakers.
Essential first steps
Language Shyness among Heritage Speakers with a link to Stephen Krashen´s short but indispensable article on the topic.
Your heritage speakers think you are weird on expanding your students language community
Un señor muy viejo con unas alas enormes (Embedded reading, links to two films, adapted version of original text by Gabriel García Márquez, comments about teaching vocabulary in context)
En el fondo del caño hay un negrito (description of how I taught this short story, along with several supporting activities)
Let me be frank: compelling reading had a far bigger impact on my students writing than any explicit spelling lesson. Nonetheless I am including these lessons about accents because they helped me, a non-native speaker of Spanish, develop a certain authority in the classroom. These are lessons that we do early in the year and then refer to in 5 second grammar pop-ups throughout the year, mostly as a way to draw their attention to spelling. Nonetheless I am convinced that student spelling improves through reading, not through mechanical exercises like these.