- September 1, 1988
- September 2, 1988
- September 3, 1988
- September 4, 1988
- September 5, 1988
- September 6, 1988
- September 7, 1988
- September 8, 1988
- September 9, 1988
- September 10, 1988
- September 11, 1988
- September 12, 1988
- September 13, 1988
- September 14, 1988
- September 15, 1988
- September 16, 1988
- September 17, 1988
- September 18, 1988 (This strip is adapted in Why, Charlie Brown, Why?)
- September 19, 1988
- September 20, 1988
- September 21, 1988
- September 22, 1988
- September 23, 1988
- September 24, 1988
- September 25, 1988
- September 26, 1988
- September 27, 1988 (The day that It's the Girl in the Red Truck, Charlie Brown first aired)
- September 28, 1988
- September 29, 1988
- September 30, 1988
| ← August 1988 | October 1988→ |