Tyra Heman (R) a senior at Marjory Stoneman Douglas High School, holds a sign that reads, 'Enough No Guns,' as she is hugged in front of the school where 17 people that were killed on February 14, on February 19, 2018 in Parkland, Florida.

Yesenia Herrera, a first grade teacher in Boston, has undergone training that helps teachers assess when they should flee, lock down or try to fight back during an attack.

However, she said she does not think teachers should be armed, a subject that's been hotly debated in the wake of the Parkland, Florida massacre. As part of his strategy to deter more school shootings, President Donald Trump has said he wants around 20 percent of the most "gun adept" teachers to be armed.

Trump tweet

"I'm not a soldier," Herrera told CNBC recently, a sentiment voiced by a number of teachers around the country who are nervous about having weapons in the classroom. "I can't even imagine myself being a soldier . . . I picture myself getting my kids out of there or hidden."

Yet Trump's proposal is perhaps easier tweeted than done. Putting guns in the hands of teachers is a concept that's widely opposed by educators like Herrera, and very costly to boot.

According to the National Center for Education Statistics, there are nearly 3.6 million teachers in America. That makes arming masses of teachers difficult at best – or as a Brookings Institution report put it recently, "entirely impractical" at worst.

Cost is just one reason why some analysts feel arming teachers isn't feasible. Recently, Brookings analyst Michael Hansen put the price tag at an "extremely conservative" estimate of $650 million, or nearly $1,000 per teacher annually.

A key element is the training each teacher would need to wield a weapon. The price of getting a permit varies greatly from state to state, running as little as $10 in some states – or over $100 in others.

In a comprehensive analysis last month, The Washington Post found that under certain scenarios, training and arming U.S. teachers could cost as little as $43 million, or as much as $1 billion.

Regardless of the cost, a growing number of teachers appear uncomfortable with having guns in the classroom based on principle. In a recent survey, the National Education Association showed an overwhelming majority of educators oppose the idea.

"A teacher's job as an educator is to nurture, uplift and inspire," Tommy Chang, superintendent of Boston Public Schools, told CNBC in a recent interview. "The thought that teachers should be armed in order to ward off violence is utterly illogical and will result in making our students and teachers less safe."

William Hayes, who used to work at New Mission High School in Boston and now is the principal at Mastery High School in Camden, New Jersey, said he got into education because he has a passion for young people.

He wanted to have an impact on the future leaders of this country, and that vision didn't involve using a weapon.

"Teachers are already asked to do a lot," Hayes told CNBC, raising concerns about where the funding would come from. "We play many roles . . . we are not equipped to provide teachers with guns."