During one of my searches for best practices, I came across some really nice resources in New Zealand called New Zealand Maths. The site is actually for teachers in New Zealand but it has some lovely materials that can be used in different grades.
First is the resource finder which has a searchable data base using curricular levels, numeracy, or Pact aspects.
Although there is a section on lesson planning, it requires you be logged into the site to use everything.
The third section is on Numbers and Algebra. The number part covers strategies, knowledge and a section for the teacher discussing the sequence progressions. Although many of these activities are for elementary, there are some good ones to use for differentiation and scaffolding. I checked one out on square roots and cube roots. It includes a process to see the relationship between squares and square roots, cubes and cube roots.
There are also sections for Geometry, Measurement, and Statistics. It has the same type of activities for each topic. I like that there is a section on problem solving and a separate section with rich learning activities. The rich learning activities provide a context for the math while the problem solving activities helps reinforce both the concept and problem solving
"Take This" are short activity which help springboard students into the mathematical idea and they take something with them. For instance, for one that uses a cafeteria menu, they include a variety of activities according to strand. In geometry, they are required to design packaging for the foods while in algebra they are creating problems using the order of operations.
They go so far as to include a list of picture books for earlier grades that deal with mathematics and some suggestions even have the associated lesson plans. The first suggested book under geometry middle elementary is "A Cloak for the Dreamer" by Aileen Friedman and published by Scholastic. This could easily be used in middle school with students who are lower performing. It could also be used by older students who could go into a lower elementary class, read it and help run the lesson.
So many possibilities.