We have "Play it today" in our family, it covers a lot of material and comes highly recommended. There are 40 booklets accompanied by 40 tapes, and were available in the early 80's (orbis publishing).
The lessons start from the assumption that you have never played a piano/keyboard at all, it all starts from the basics – and that’s fine. Then moving to lesson 10, for example, brings in octaves, accidentals, G major scale etc. Lesson 20 will be more advanced of course, and bring in advanced scale/chord structure/harmony. The Penultimate lesson (39) gives you Fur Elise to play - and it is assumed you can play this piece with comfort by lesson 39 – you are well prepared. There are harder pieces than this though in the earlier lessons, and lots and lots of exercises, chords, styles (classic, pop, jazz, R&B - name it - its there)
Best thing about the course, is all the material you see in the books are on tape - so you know what it sounds like beforehand - about 20 hours of it. It's designed for the player who wishes not to fork out £100's (thousands?) on piano lessons, though a teacher would help in times of need I guess. The Course itself costs my brother about £170 when he brought it 15 years ago - and if you can get hold of it - it comes recommended - even “pop stars” have had a go at this one! (Danny Schogger, session musician for WHAM!, George Michael, ABC, Steven tin tin Duffy and Hipsway, amongst others).
The great thing about the course, is not the grades/pieces etc, but the overall content. Over 500 pages in 40 booklets give you almost all styles imaginable - but “leans” towards the "classic" (thank you!), and takes down that line. It's my feeling that these 40 lessons would be suitable for almost anyone, it shows you how to play the piano - BUT WITH NO SHORT CUTS!. No
"Play the piano in a week" nonsense here

There are many methods around, but to me, the best ones are those that give you lots of work to do - and not wanting for a “great” deal more once you’ve finished. - You can always learn graded pieces after you’ve finished the course – you’re sight reading will be spotless – if you stick to the letter that is! “2 years for completion” of the 40 lessons are mentioned in the introduction booklet if memory serves me correct – even quicker if you put more than the suggested 30 minutes a day in
AnthonyB