Just draw your letter of choice and place squares of color down along the line of the letter. Then have kids place blocks down on each square. Start from the top if possible.
Physical or Occupational Therapists may place the letter on the wall and each time a child does an exercise, they will place another snap block (you can use velcro also) on the letter.
Share what is working for you by submitting work on your brilliant therapy facebook page and encouraging a friend to join (it is @.65 cents per day) and see what new things are added every week.