We've used Vocabulary from Classical Roots:
https://www.amazon.com/Vocabulary-Classical-Roots-Nancy-Flowers/dp/0838822525Nominally, grade 4-11, with one softcover book per grade. The grade 4, 5, 6 books can reasonably be used as write-in workbooks. The grade 7-11 (A-E) books need separate paper. There are 16 lessons in each book (plus reviews every other lesson for levels A-E, so 24 lessons, really, for those levels), divided into about 5 mini-lessons/exercises, which will usually take about 5-10 minutes apiece to do at the elementary level, more when exercises involve applying vocabulary in written exercises (usually at the secondary level).
Although one can blow through these exercises very quickly, skills are more likely to stick through many short sessions, than fewer, longer sessions.
