- Learning Curve
- 1992-1993 pre-production models: (staples, flat magnets, undated wheels, yellow outlining)
- (white outlining, no staples, flat magnets, undated wheels)
- (white outlining, no staples, round magnets, 1994 wheels)
- 1996 (smaller round magnets this year only, rounded funnel, new face, 1996 wheels)
- 1997 (thicker 1997 wheels)
- 1998 (1998 wheels)
- 1999 (plastic funnel, smokebox, and coal, 1999 wheels)
- 2000 (2000 wheels)
- 2001 (2001 wheels)
- 2002 (removed ledge, 2002 wheels)
- 2003-2010 (2003 wheels)
- Douglas' model has no funnel.
- While his brother Donald was retired in 2009, Douglas wasn't retired until 2010.
- Despite being featured in the Working in the Trainyard and the Mountain Adventure Sets in the 1997 yearbooks, his tender was not included.