Hi Bob, I have to teach recorder and baby keyboard in high school music lessons, to around 20-30 students in each class

It wasn't easy but I found the best way to do this (like exactly what whynot said) is to learn from doing or playing, learning from experience is what they love. All I do is first I get a recording of the song we're going to learn in its original state, I then make melody + piano accompaniment sheet for the class, sometimes I also have a counter-melody or harmony line for them to divide into parts if they can get the original melody perfect (they love this

), I like choosing songs with an intro of usually 4-8bars, so I can play that on the piano and count them in. I choose songs that the kids can relate to, for year 7-8 kids I choose themes from movies and tv series, cartoons etc...
I have done recorder and piano accompaniment arrangements and one-hand melody lines for piano or voice, + piano accompaniment, and I compile into book format, so I can just go into the class and revise or learn new pieces

The books are categorised according to difficulty, for example, for recorder arrangements I will introduce new notes every lesson, I will introduce more complex rhythms and even accidentals by looking at new songs with these concepts (you make the arrangements so it can be suited to what you want to teach, you can always add new elements into arrangements ie dynamics, key signatures, expressions etc once they know the basics)
I don't know how old your students are but I do teach notation from the start, if they can read pretty well they'll understand note names and look at the pattern on the stave fairly easily, I have recorder charts and keyboard pictures on the board for them if they are not sure where the notes are. I get them to first write the letter names above the notes on the stave from the charts, (I will eventually get them to only write certain notes ie all C and Gs on the stave, they will need to practice at home their set pieces and also reading skills because I constantly assess their progress with mini quizzes, they love practical exams

The lessons goes like this
*clapping exercises (imitating my rhythms)
*revise note values, put up 4 choices on the board for 4 different rhythmic patterns, get them to listen to each and repeat each like an ostinato, divde them into groups, and doing 2 or 3 or 4 at the same time (depends on their abilities), later on you can do rhythmic dictation, or even pick out which order you clapped the 4 patterns etc.... lost of possibilities, believe me, these will become a favourite routine for them and you can use body percussion, or percussive instruments for these too, it won't take long, this exercise when it becomes routine
*revising old notes learnt by first playing, then getting students to come up to the board and writing them on the stave, and demonstrating it on their instruments...the class imitates too, this will eventually become like a short scale exercise for warm up

, you can do games with this, like point and play, imitating by sound alone, composing a short melody for a partner to play etc...
*on with the new notes and pieces, explain and show what new things to learn for today and goals to achieve on the board with specific details, (and also minutes in your own head for each exercise) then bashing through with sightreading
*practice piece as a class section by section, line by line, and divide the group to hear individual progress, then playing with piano accompaniment etc...
of course this will build up their repetoire and then whenever they want, they can pick a piece from their folders and play as a class

The main thing is lesson plans and organisation, know exactly what is to be achieved from the class, even if its just experiences they will get...
I guess classroom management or group management skills are vital, you have to connect with the kids but still let them know who is in charge and all the rules

make the lessons fun with cool repetoire they love, group and individual work (healthy competition), roles and specific goals they have to take/achieve, and finally learning music as another language to express and communicate with. I guess its a little different with my situation in a classroom in high school, if I get through to 10 kids out of the 20 I will be happy, you always have to include the students and not exclude, sometimes you might find yourself unconciously excluding some....but sometimes kids exclude themselves with no participation and disturbance because they are not interested with music, your goal would then to involve them specifically with a project, make them the conductor or percussion player within the ensemble and jobs like that...
With the catching up of work, make sure you say to them it is their responsibilites to come to you for any missed work and and new songs they haven't learnt, you'd be surprised and what kids can teach each other, they want to show their friends what they've missed and fill them in, if they don't do this, don't worry, it is not your responsibility to chase them up for work they've missed, it is impossible if you have several groups and a lot of students in each. It is always good to make CDs or tapes for songs they will be learning, so even catching up by imitating and listening is better than missed lessons....

goodluck Bob, hope this is of some help...