My school uses "Math Expressions". There are formative assessments to be done orally at the end of each lesson. I typed up each formative assessment and give them to every student after each lesson, unless there is a quick quiz/fluency check. There are many formative assessments that ask the students to write an explanation, which is good practice for tests they will take in the future. I grade each assessment with a simple 3, 2, or 1 and use those to group my students. My groups are constantly changing based on their scores from their assessments. I keep all of their formative assessments at school - I don't send them home. My students' written expression has improved since doing these.