I get asked this question a lot.
A friend who taught for Match, now doing Peace Corps, wonders about grad school (an M.Ed) upon her return. Should she go?
I don't know. However, I would say...
Grad school is 6 things.
1. On-your-own intellectual development. You do that by talking to classmates and a favorite professor or two with whom you get quality time, reading stuff, attending panels, etc. Theoretically you can do this for free. But a masters is a protected 9 months.
2. Classes. You'll take 8 to 10 in a year. Two will be quite good classes and will bolster #1, the on-your-own intellectual development. A few classes will be okay. Some will be frustratingly bad. Buying these 8 to 10 classes is probably the worst reason to do a one-year masters. Particularly as MOOCs emerge, and you can get the lectures for free, if you're disciplined.
3. A credential. The best edu-organizations don't care much about these, particularly if you already have an elite brand undergrad education for signaling. They care about your track record much much more.
The rest (95%) edu-organizations DO care about this. Elite university brands matter in particular for non-teaching edujobs.
3b. If you want to teach in a district, know that they typically pay extra for someone with a masters (even though there's great data showing the degree has no linkage to children actually learning more). In this case, it's almost automatically cost effective to have a masters degree, but not essential to have a prestige university brand versus a cheaper state school.
4. A network. Both the immediate friends that you'll know, plus sometimes alumni you can contact. Strongest with elite universities.
5. Down time between 2 jobs, and a chance to have fun, go on some dates, etc. This is legit! Summer camp for adults with nobody raising eyebrows that you're a slacker. I had a lot of fun in grad school.
6. Debt plus opportunity cost. Figure both out. If you forgo a $60,000 per year job, and borrow $40,000 to attend, the true cost of a one-year masters is $100,000...not $40,000. If you decide on a TWO year masters program, you just doubled the true cost. Don't make that decision lightly, unless Mom and Dad are paying the whole thing, which implies they got a lot of dough, which makes it fine to blow their money.
As you consider a masters degree program, try to break down the decision into 6 component parts. Be honest with yourself about what you want.