Adding to bx's succinct recovery arm progression (excellent), we (TI) have recently adopted progression for stability and whole body movements and position that has been *very* effective - and is used in 1.0 workshops.
Coaches start swimmers in 1. "Torpedo" (no kick) to get head-spine aligned and learn to balance over lungs without the aid of arms in front or kicking for stability, 2. "Superman" arms in front adding to stability and balance while maintaining head-spine-hips alignment, 3. "Slot to Skate". This is probably the most effective since it places the body in position where entire body fires together finishing on a clean edge (skate) and 4. "Superman to Skate". Now learning to hold the edge, with tone vessel-core stability, level and balanced after the "switch"
The first four sequences have proven very effective for swimmers (of any swim level) to learn and achieve core stability as well as integrate the timing of the switch where entire body fires for whole body propulsion which integrates into your freestyle quickly.
It's all laid out very well, easy to follow and complete in eBook and downloadable demos, step x step, Effortless Endurance Self-Coaching Course: Select this link to review: http://www.totalimmersion.net/store/
Happy Laps and Core Stability!