This is a really tough concept for Spanish learners.  One activity we did with the "rules" of Preterit vs. Imperfect was to categorize with sentence slips. They were in pairs and everyone got a brown sheet and a baggie of slips of paper (thanks to my wonderful TA).  Their first job was to sort YELLOW slips, the "rules", into which category they belonged to.  I nudged and questioned and checked and then they moved to step 2. Step 2 was using PINK slips (Sentences in Spanish) into categories.  This was easier to start with because they could see the verb in Spanish. Step 3 was placing YELLOW rule slips outside of pink slips to defend their reasoning (this took it up a DOK I believe).  I just set pink oustide of yellow as an example.  It works both ways. Step 4 was using BLUE slips (Sentences in English) to categorize and match with YELLOW on the outside to defend.  This was harder because they really had to know why since the sentence was in English.  The English sentences were different than the Spanish ones, so it didn't turn into a memory task. Step 5 was spreading out YELLOW (Rule) slips out like category headings and placing both PINK and BLUE slips under which rule they fit.  We didn't use the brown category paper here, just make small categories. Students felt like this really helped and I thought it helped kinestetic learners as well as students who weren't really 100% on the topic. Here is the link to these documents:  (I just used different colored cardstock.) Preterite vs. Imperfect Paper Slips