When most public school teachers want a raise, it's not as simple as negotiating with the principal of the school.

Most teacher salaries are based on previously-agreed upon scale negotiated between the school district and the teachers' unions.

Teachers in Pueblo City School District 60 went on strike on Monday as negotiations for higher pay have failed.

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Based on data collected by the Colorado Department of Education, teachers in Pueblo D-60 have an average salary of $47,617.

The teachers are paid based on a "step and lane" chart; a pre-negotiated pay scale, though the Pueblo Education Association said it is working on an expired scale that carried over from the previous school year because of failed negotiations.

The Pueblo D-60 pay scale ranges from $35,277 to $73,232, based on years' experience and continuing education.

The way the scale works is that the more years you have taught, the higher step you land on. The more continuing education you get credit for, the farther to the right on the scale you move, thus receiving higher pay.

This is how most teachers in public schools get paid; a chart called a "step and lane." You generally move up a step each year, and get more pay. If you complete continued education, more pay.

INTERACTIVE | Average teacher salary in each Colorado district

For another example, the average teacher salary in the Boulder Valley School District is $75,220, but the "step and lane" scale ranges from $44,812 to $107,011.

The Colorado Department of Education tracks the average salary of 178 school districts. CDE receives the actual salary of each teacher and provides an average on its website.

Pueblo teachers went on strike after rejecting the school district's most recent offer.

One-thousand teachers in Pueblo have left their classrooms for picket lines. They want a pay raise.

The district offered a cost of living increase of 2.25 percent effective in September. That would bring the salary range to $36,070 to $74,879. The district also offered a one-time bonus of two percent ($705-$1,464, depending on the teacher's salary), or one thousand dollars for each teacher.

Pueblo teachers said no to the offer. They have previously said they are seeking a two percent pay increase retroactive to the start of this school year. That means instead of a scale ranging from $35,277 to $73,232, the teachers would be paid $35,982 to $74,696, and then they would want to negotiate 2018-19 based off that baseline.