As Ammin mentioned, first you need to find out the aims of the course, as you might not have to include speaking or listening.  But if you do, try:

Drawing on the texts to create speaking exercises.  

My wife teaches young teens from a book called New Concept English (originally written in the late 60s or early 70s if I'm right).  Basically every unit follows the same pattern:  a single two-paragraph text accompanied with a picture, several multiple-choice grammar exercises.  So every week we sit down together and brainstorm different ideas for speakin tasks based on the text, after which she takes the best idea (or best two ideas) that we came up with and her classes go great.

There are 3 main, easily adaptable, tasks you can springboard into from a text.

• Story Telling.
  This can be written or spoken, and there are many ways you can do it.  Try getting the Ss to create the story of what happened after the text; what happened before the text; a similar story with different characters; re-create the story based on how a main character with a different personality type would've dealt with the situation; choose a minor character and create his/her side-story; change the ending; come up with a similar story based on your own life.  All of these use ideas and themes from the text that you've already had the students study and read and this often means that even the weaker students can come up with something.
• Role Play.
  As with the Story Telling you can create all kinds of different role-plays depending on whether you draw on the characters, the situation, or the languag.  Have them role-play the main character and a reporter interviewing that person; or have them role-play two characters; a psychologist and one character; have them create an entirely new role-play based on the same situation; have them pick two sentences from the text and include those in a made-up role play; etc...  Try out different variations and see what works best with those Ss.
• Discussion Questions
  Simply make up 5 questions before the class that you intend Ss to discuss - personal questions or opinion-eliciting questions based on themes from the text.  (ie. If it's a text about a plane crash you could use 5 of:  1) Have you travelled by plane to another country?  Do you think driving or flying is safer?  Why?  3) Would you travel on a 6-seater plane?  4) Have you seen 'Lost'?  5) What would you do if you knew your plane was going to crash and you had 10min left?   6) Would you like to be a pilot?  7) How about an Astronaut?)

Use different combinations of these each week and you should get a response, especially if you build up the situation and context through boardwork (drawings & words) and questions before they start the task.

Dictation /Teacher Reading Aloud

Try different ways to give them listening practice by introducing things yourself.  If you have several questions or a vocabulary exercise you want them to do, you can throw in some listening practice and save paper at the same time by telling them to pick up their pens, saying, "Write everything I say, but when I say 'gap' just leave a space...  one... Last night I ...gap... dinner.  Then I ...gap... for a walk.  While I was... gap.. I saw Bill."  etc...  Once they've finished writing, have them discuss the quesitons or complete the exercise.

Instead of using the books core texts for reading only, turn every third one into a listening by reading it aloud - do it like you're a real story-teller.  Don't overdo the voicing, but a slight change for 'the narrator' compared with character's speaking.  Lots of pauses and heavy intonation to build up interest and engage them at interesting points in the text, etc...

Setting the Context

Often teens will appear to be bored and uninterested... and if they think of the lesson as 'studying English', they'll definitely be bored.  So to get them thinking of the lesson as 'having a chat and reading about things related to our own lives', really work on the context.

If you have a stale technical text about agriculture and irrigation, start off:

1. What did you have breakfast Susan?  How about you Andy?  Bill?
2. So where does the rice for your congee come from? 
3. Have you ever been on a farm?
4. Would you like to work on a farm?  How about owning a large farm in Australia - you'd be rich and you could ride motorbikes around the fields?
5. What kind of equipment do farmers use?
6. What can they do if there's not enough water for the crops?

And that leads into your reading question... "We're going to read an interesting text that tells us what farmers do to water their crops.  You have 2min to read through it quickly and find out what they do.  Okay?  Open your books on page x... go, go, go, quickly!"

The more context they have, and the more they feel that the language is part of their lives and/or can be used to talk about their lives, the more engaged they'll be.

Next up, you'll want to find some good techniques regarding disclipline and behaviour... 25 teens - tricky!