My collaborations with psychologists began with Hanna Levenson at Texas A&M. Her comments when we finished a walk through the old, cavernous, 125-student general chemistry laboratory forever changed the way I view student interactions in school labs [1]. Carol Tomlinson-Keasey (most recently Chancellor at the University of California, Merced) [2] introduced me to cognitive science, and, together with Robert Fuller at Nebraska, to the ideas of Piaget [3].

It is not surprising, then, that my most recent collaboration with Duane Shell led to development of the unified learning model (ULM) [4]. Ours was not really any kind of a discovery as much as a synthesis from the existing literatures of several fields (psychology, educational psychology, and neuroscience). When fields develop separately, unique vocabularies emerge to describe similar or even identical phenomena. It's similar to using chemical periodic tables printed in different languages [5].

Here are the sound bites we use to describe the ULM: Learning is a product of working memory allocation; working memory's capacity for allocation is affected by prior knowledge; and working memory allocation is directed by motivation. The ULM enumerates five learning rules: New learning requires attention; learning requires repetition; learning is about connections; everyday learning is effortless but school learning requires effort [6]; and learning is learning. (The last rule has to do with neuronal changes on the cortical surface being cellularly and biochemically similar to one another.)

Because science was once taught as memorized facts, I know for sure that "the state in the center of the earth is igneous fusion." I had no idea what "igneous fusion" meant until the early 1990s, when it dawned on me – molten rock [7]. I was in school when Sputnik flew, so I did not benefit from the resulting curricula like Chem Study [8]. Thought to be too abstract (formal), those curricula were replaced by an onslaught of hands-on curricula [9].

I watched as the National Science Foundation education group was dismantled because exception had been taken to one curriculum (MACOS) [10]. I watched it being rebuilt, first under the guidance of my friend, Bassam Shakhashiri, who wears the button "Science is Fun" [11]. Well, yes, science is fun! Scientists solve puzzles. Sometimes those are very important puzzles. Inquiry is about the puzzle-solving part of science, and it's fun.

But don't kid yourself; science is also hard! Everybody knows that [12]. Kids know that. Parents know that. You may like science very much, and think it is great fun and very worthwhile, but you know that, too.

Forget all this stuff about "rocket" scientists and talent and inborn "gifts." Many, many more people can become good at skilled areas (sports, carpentry, music, dance, science, medicine) than are good at them. They would have to work at it and have the right kinds of support. It took a long time for me to come to believe that [13]; like most Americans, I bought into the idea that being good at science was a "gift" and that there were such things as styles of learning [14]. In STEM there's a need for many experts [15].

What we load into working memory are chunks – probably just three or four of them. Worse, we only look at one chunk at a time, the focus of attention [16]. Experts have big chunks. If you want to become a STEM expert, you need to develop big chunks in a STEM area. That's true no matter what kind of expert you want to be – golf, physics, piano, history.

Here's the STEM difference, and it's a big difference. In some areas, it doesn't matter in what order you acquire those parts of a chunk that will become your expertise. Further, you can start first on those that interest you most, and they will likely stimulate greater interest in those that don't interest you at first. That's not how it works in STEM areas; sometimes you must know one thing before you can know another thing [17]. Further, it is hard to have an immediate personal interest in some of that early-stage knowledge; driving early learning with that promise of distant personal interest is difficult.

The last couple of decades have seen a few good things in science education. Igneous fusion (the memorize-and-regurgitate curriculum) has largely given way to inquiry (puzzling), which is good and reflects the fun part of science [18]. K–13 teachers have been stressing the interest and enthusiasm of the moment, the so-called situational interest, possibly in the hope of incurring some personal interest [19]. What is bad and has been lost, however, is reminding students that science is hard and that it is hard for a reason. You must know a lot of things to become expert, and many of those things must be learned in a certain order.

Why would I want to do anything that was hard? Well, here are two really good reasons. First, like most people, if you work at it, you probably will succeed and become expert at it and earn a living. In science, once you've become expert you can spend your life solving interesting puzzles. Not all of life's ways of earning a living are interesting. Most scientists do interesting work.

I've never taken a biology course (nor an education course, for that matter). I went to a technical high school, and majored in chemistry at college. Chemistry is a lot easier than biology. In chemistry, you're pretty sure of what to put in the flask. So long as the flask itself doesn't react, you're OK. Field biology seems to me to be a lot tougher; you're never quite sure what's "in the flask" and what's not, so to speak [20]. That can make puzzling a lot more interesting. Chemistry is interesting; biology must be even more interesting. I can't imagine teaching a biology course that was dull. If I were a biology teacher, that's what I'd be emphasizing. At the same time, I'd stress the math and statistics and chemistry that I would need to know to be able to answer the questions that were puzzling me.

Like my best teacher, Gilbert Stork [21], I'd be trying to ask these questions of myself out loud as I taught. (And I probably wouldn't talk for more than 20 minutes a week, and make a minimum score on a repeatable test the price of admission to hear me talk.) More than once, Stork, a renowned synthetic chemist, would point to a structure on his chalkboard, and then point out the window to a tree and say something like, "The sun is shining, it is 7°C, and that tree is making these molecules right now; with all the stuff and gadgets we have around here, we should be able to figure out how to do it, too."

These are too numerous to list here. Please see; the numbers correspond to those I have used as citations above