The SN401 stereo headphone is an ideal budget selection for the classroom.

About this headphone:
Flexible, adjustable headband
Beige color with black earpads
Wipeable leatherette earpads
4 foot cord
Stereo straight plug for easy insertion into devices
Great sound quality for the price!
Individually packaged in sealed plastic bag
3.5mm stereo straight plug
Great for testing and other classroom/library use

Electrical Characteristics
Speaker element type:  Ferrite
Impedance:  L:  32 ohm  R:  32 ohm
Resonance Frequency:  L:  160 Hz  R:  158 Hz
Sensitivity: (avg 600/800/1000/1200 Hz)  L:  99 db/mW  R:  100.3 dB/mW
 (20-20,000 HZ)    
Output @ 50 mW:  L: 104.7 db SPL  R: 105.0 dB SPL
Harmonic Distortion     100 Hz
(3rd@5wW)      500 Hz
        1 kHz
Left/Right phase:  Wired in Phase

3 month limited warranty