You obviously have no facts on the case in Oklahoma. First, the school boards almost all approved the walkout, making it a walkout not a strike. Second, Teacher pay in Oklahoma is terrible and has been for a very long time.
What finally pushed them over the edge was after being promised to have additional funding for years, every year over the last four education has taken MASSIVE cuts in funding. The current education funding in Oklahoma is lower in real dollars than it was 15 years ago. The funding situation is so bad that a quarter of the schools in the state only hold classes 4 days a week. The walkout started on the day the legislator by law had to fully fund school, which they didn't do.
Oklahoma has continued to push unfunded tax cuts year after year. Almost all of those tax cuts have been in the form of tax credits and exemptions to well off people. The capital gains exemption (no capital gains tax on Oklahoma businesses) alone costs the state $115M/yr and 89% of it goes to the top 1% of income earners. They have also made DOT funding the highest budget priority so it gets funding before education, health, etc, but they hadn't raised the gas tax since the 80s and it was the lowest in the country (they finally raised it by 3 whole cents). It also doesn't help that during this time the republican administration has authorized the creation of tons of new school districts so every tiny town has its own system (over 550 in the state).
The OKC school district has been averaging an annual turnover rate of 25%. One of the best school districts in the state (Edmond), has said they will need at least 300 new teachers next year to cover attrition and growth, but the entire state is only going to graduate 309 new teachers. Last year nearly 2000 teachers were certified through an emergency certification process because they were not actually qualified to be teachers.
The state constitution is also ridiculous in that it takes a 75% vote of each house to raise taxes, but only a simple majority to cut them. So even during a time when we've been having billion dollar budget gaps, they keep cutting revenue, while not raising any. Further, the only things republicans are willing to vote for are regressive taxes.