Are you careful not to touch the glass with you bare hands? You really should use latex gloves. The oil from you hands getting on the bulb will cause the filament to burn out much faster.

I've used some "superwhites" on my motorcycle. I forget which brand, but they lasted over 30,000 miles and were definitly brighter and more white in color that the standard OEM H4 bulbs. Sicne hte headlights are on all the time like in the school bus, I'd estimate that they saw 800 hours of operation without replacement. That would probably be the equvalent of 6-8 months on the school bus. SO 4 months is a little short, but i suppose 1 year isn't unreasonable. Most normal vehicles don't see 30+ hours of operation per week.