Beginners and Intermediate Students

I teach my beginners and intermediate students "guide notes" first.
I start with middle C, high C, low C, G form G clef and F from F clef . Form there, we start reading short pieces with seconds only. They are not supposed to name the other notes (around ttheir guide notes) but just describe them as "second up, second down". After they master that, I inroduce the thirds , fourths and so on. The same thing applies to the guide notes. After they master the mid C, low C, High C, F and G, I add another set at a time: low G (from F clef) and high F (from G clef). Next, I add what my kids call high-high C and low-low C. we keep using the same strategy adding one interval at a time.
For rhythm, I make them tap both hands together from the beginning. If they can play hands together, they can tap them together too.
As they improve, we start "mapping" the pieces (always short). They have to draw lines for both hands that describe the movement and rhythm of their music. I let them use their imagination as far as their maps go. Each student is different. These maps are also great to memorize pieces.
I use a book which was suggested to me by an OMTA adjudicator called "Accelerando". They have a series of progressive technical exercises (always two lines long) with rich rhythms and key signatures. I realy recomend them. They sound very nice two. My students love them!

Duets

Duets are a wonderful way to practice sight-reading.
The first duets I use are Pozzoli (the Italian composer, not the Mexican soup) called "Sorrisi Infantili" and Diabelli "Melodious Pieces". They are all in 5 finger position. At this point, my students are also practcing 5 finger patterns in all keys.
Later, I add Kabalevsky's "Favorite piano duets for beginners" and Dello Joio's "Family Album".
There is an amazing selection of nice duets from the 20th century and contemporary composers.
The next step should be learning scales and modes and mapping those as well.