Some Solutions
I've used the first three of these. They work. They each have different pros and cons. I actually like all three of them for different reasons.

The Richard Solo 1800 for iPhone (iPod Touch) will recharge the device to about 80% rather quickly and includes a built in LED light and laser pointer. I like that it clicks into the device. You can continue to use the device with the battery connected without worrying about it falling off.

The Richard Solo 1200 for the iPhone (iPod Touch) has slightly less charging capacity, includes a little LED light, and costs less than the 1800. This battery also connects to the bottom of the device but can very easily detach. It is small and has a nice hard case.

The Solio comes in several models and is unique in that it is a hybrid charger that can be recharged by the sun light or the wall outlet. This solar feature is ideal for the backpacker or more rugged camper.

I have not tired the Morphie Juice Pack, but have seen it in action and heard good testimonials about it. Fitting snugly on the device, it will not call off easily. Several different versions are available.

This is a link to the complete post about using wireless mic systems with your computer to record podcasts. This post only presents a few wireless microphone system options. These are not recommendations but are presented to help you get started in your search for a solution that will meet your needs and fit within your budget.

Wireless Microphone Options

Memorex VHF Wireless Handheld Microphone - MKA381
• Available from Target.com (product link) or your local Target store for around $20 as of this writing
• This microphone is in the toy department for karaoke. But, I was so shocked to find a $20 wireless mic, I bought one to see if it would work at all. It did--with limitations. You will have to determine if it would meet your classroom needs.

• Additionally, you can find any number of other handheld and lavaliere wireless mic system options from Target.com at this link. They are all cost more than $20.

Wireless Lapel Microphone System
• Available from RadioShack.com (product link) for about $50 as of this writing.

• Additionally, you can sift through this link at RadioShack to find other handheld and lavaliere wireless mic system options that are more expensive. This link also includes bluetooth devices, which, while they have special considerations (see end of post), can be used as well!

Audio-Technica 88w
• Available at B&H Photo and Video (product link) for $169.95 as of this writing. We used this mic at Mabry when recording movie projects. It is rather durable, has 2 selectable frequencies, has an omni directional lavaliere mic*, and can be monitored through a head phone jack.

Telex Wireless Microphone Systems
• Available at B&H Photo and Video (product link). These are more expensive, higher end wireless microphone systems that range from $559 to $789 depending on the mic(s) you select. (You would definitely want to lock this up at night!) This Telex system has over 1,100 frequency/channel combinations using UHF (better) instead of VHF, diversity reception, all three mic types are available, and ClearScan technology that tells you which of all of its channel options is receiving the least level of signal interference.

Bluetooth

Now, this is totally different, but... Don't forget the bluetooth headset you use with your cell phone! It too can usually connect to your computer, if your computer supports bluetooth devices. The Macs running OS 10.5 (and perhaps earlier versions?) all do.

*An omni directional mic will pick up sound from around the room, not just the sound spoken directly into the mic. This type of microphone has advantages and disadvantages.

Mics basically come in two flavors: directional and omni-directional. A directional mic records what is directly in front of it and more or less ignores sounds around the room. An omni-directional mic, on the other hand, records sound all around it fairly equally. This microphone is both omni-directional: good for recording whole class activity, and can be switched to directional.

I am told that the mic plugs into your Mac or Windows USB port and requires no additional software: easy set up and use. For most school budgets, it's probably too expensive for a "class set" of mics. I've seen them: they are not small. I'm told it sounds really great.