Then one day I hit upon the Steps Method set on USCF Sales site, Step 1 to 5, manuals and workbooks. I was immediately hooked. This is the books I am looking for, and the large amount of exercises are appropriate homework for my students.
For each Step, there is the Workbook, extra Workbook, and plus Workbook. Each contains 500+ problems, which means to pass each Step, a student has to finish about 1500 problems. There are 5 Steps, so total 7500 problems. If a student can finish all of them, plus some game playing experience, definitely s/he can reach 1500 or above. It's a very concrete plan. There is no need to scrap up other material. After s/he reach 1500, s/he is good enough to pick opening repertoire, study positional thinking, and do end game training.
Learning chess is a long term process, taking a couple of years to reach 1500. With a good game plan, we will reach there.