Veteran science teacher David Spahr said he would never want to be like the guy who told Albert Einstein he wasn't good enough.

So when he sees one of his students struggling, he remembers something he's learned from them time and again.

"Just because they're not shining today doesn't mean they won't shine later," he said.

Mr. Spahr has seen countless students come through his classroom. If they're aspiring scientists or less skilled students, Mr. Spahr seems as excited to teach them as he likely was a half-century ago. And he's still learning from them.

The Baldwin High School physics and chemistry teacher, 74, celebrates his 50th anniversary as an educator this year.

Energetic andloquacious, Mr. Spahr -- a Pittsburgh native and graduate of Penn State and Rensselaer Polytechnic Institute in Troy, N.Y. -- is clearly passionate about science. In 50 years, he's witnessed remarkable changes in his students, technology and even education itself.

He certainly isn't old school.

Mr. Spahr posts assignments online and occasionally shows students episodes of "MythBusters." Initially hesitant, now he's sold on the high-tech interactive whiteboard the administration ordered for science classrooms five years ago.

Even while embracing new technology, Mr. Spahr still peppers his lectures with colorful, and sometimes esoteric, history lessons.

"He's an entertainer," said Dee, his wife of 47 years.

The historical references aren't surprising -- before he began teaching science, Mr. Spahr had a brief stint as a U.S. history teacher after earning his degree in chemical engineering.

As developments in technology have undoubtedly changed the classroom environment, so has education reform such as No Child Left Behind, which Mr. Spahr said is misguided.

Also during his tenure, the responsibility has notably shifted from student to teacher. Inflating grades to make parents and kids happy, for example, is more prevalent today, he said.

And though he doesn't bounce out of bed every morning as he used to, "Thoughts of the school day bounce in my mind," Mr. Spahr said.

While discussing his former students, Mr. Spahr fired up his laptop to share an email from one who went on to study medicine. The student praised his former teacher.

"Most importantly, your classes shaped my mind to think like a scientist," he wrote. "I cannot thank you enough for these challenges."

The teacher also was recognized in 1992 by a student who was chosen as a U.S. presidential scholar and named Mr. Spahr as an inspiration and an outstanding educator.

Mr. Spahr remains markedly humble about all the praise. What's more, he admits he doesn't have all the answers. Some advanced concepts are hard to grasp, he said, and students have stumped him a time or two.

"I've found intellectual barriers that I cannot climb over," he said.

But the voracious reader -- he subscribes to both Physics Today and Physics Teacher -- said he continues to educate himself and enjoys reading biographies and the history of science.

And though he isn't sure what the future holds, Mr. Spahr has no immediate plans to retire.

After all, he still has a lot of learning to do.