Although I didn't use this entire lesson, there are some excellent vocabulary and 'anatomy' of the Constitution PDFs that would work well in lower grades and perhaps with ELL students. Good overview of the structure of government and the powers and duties of the 3 branches. I feel that there is a lot to take from this lesson to use in class.
I have used this site for years to introduce the structure of our government and more. It is broken down by grade so every teacher, k-12 will find this incredibly useful. Great visuals and a better explanation of our confusing election process than I've ever seen.
This might work nicely for comparing ancient democracies to ours today, specifically comparing and contrasting the balance of power. It is accessible enough that my 7th graders could explore it on their own.