If you have a group of swimmers who can go for at least 100 feet without stopping and are familiar with all of the basic strokes, you've got an intermediate group. You can structure a swimming class in a number of ways, largely depending on whether you prefer to focus on drills and form or on simply practicing the strokes. However you organize your intermediate class, it's a good idea to divide the lesson into a warmup activity, a main exercise or swim, and finally a cool-down and stretching.
Have the class practice isolating individual arms with the "catch-up", a variation on the freestyle stroke. To do the catch-up, keep one arm forward as you use the other arm -- the working arm -- to complete a single stroke. After the full stroke, do the same on the other side. Continue alternating sides. As an alternative, you can isolate each arm by using a float on one side. Change sides after each lap.
Stroke-specific Drills: Breaststroke
Incorporate two drills into your practice of the breaststroke. First, have students swim the stroke as usual, but hold the extended phase of the stroke for a full two seconds; this drill is called the "two count glide." During this phase, your arms are at your sides and your legs are extended; your body will glide while you hold the position. For the "two kick drill", do two kicks instead of one during each stroke. During the second kick, gently move your hands apart, letting your head and chest dip lower in the water.
Stroke-specific Drills: Backstroke
To work on the backstroke, have students practice the "single arm drill" and the "rhythm drill." For the former, as the name indicates, you keep one arm at your side and use the other arm to complete the stroke. Focus your attention on the rotation of your shoulders and your hips. For the rhythm drill, you change the usual backstroke pattern so that you stroke twice with the right arm and then twice with the left arm, and continue in this pattern.
Have your students improve their form and technique by practicing glides. Start at the edge of the pool, pushing off from the wall underwater. After gliding without any further propulsion, stand up and notice the distance traversed. Continue the gliding action, trying to improve your distance. Work on the form, keeping the arms pointed toward the far end of the pool, with the biceps squeezed close to the head. The hands and wrists should overlap, one on top of the other. The face should be directed downward, at the bottom of the pool. The toes should be pointed and the core muscles tight.