I am so excited! I taught completing the square today in my "low" grade 9 class for the first time, and I decided to try a geometric approach this time as inspired by my friend from PCMI (the awesome Danielle Soderberg*), and the kids loved it!! After just two examples on the board, they had no trouble at all working through cases with integer leading coefficients and integer vertices. It was fantastic.
Here was the worksheet I made for completing the square, and here was the warmup sheet I used prior to introducing complete the square (cut into half-sheet strips; the kids skipped the conversion to vertex form at the beginning of class and came back to that column at the end, after the lesson).
*Although, as a small disclaimer, I never saw Danielle's worksheets, so it's quite possible her approach is different and/or it is far superior. She vaguely mentioned something about algebra tiles and completing the square.