Over the past two years I’ve been mentoring a high school student, Dan
Kelly, in software development though my workplace mentoring
program. It’s been one of the most rewarding experiences in
my life, far beyond my initial expectations. It didn’t just go well,
it went extraordinarily well. One of my co-workers described the
results as, “the single most successful technical investment I’ve ever
seen made in a person.” Last week the mentorship effectively ended as
he became a college freshman. While it’s fresh in my mind, I’d like to
reflect on how it went and why this arrangement worked so particularly
well for both of us.
Students come into work for a few hours at a time a few days each week
throughout the school year, typically after school. They’re supplied
with their own computer in a mentor-arranged work space. In my case,
Dan sat at a smaller makeshift desk in my office. The schedule is
informal and we were frequently making adjustments as needed.
An indispensable feature is that the students are unpaid. Based on
my observations, the primary reason many other mentorships aren’t
nearly as effective is a failure to correctly leverage this. Some
mentors put students directly to work on an existing, funded project.
This is a mistake. Real world, practical projects are poor learning
environments for beginners. The complexity inhibits development of
the fundamentals, and, from a position of no experience, the
student will have little ability to influence the project, stifling
If being unpaid sounds unfair, remember that these students are coming
in with essentially no programming experience. For several months,
students are time sink. Maybe they fiddled around with Python on their
own, but it probably doesn’t really amount to anything meaningful
Being unpaid means students can be put to work on anything, even if
unfunded — even if it’s only for the student’s own benefit. The very
first thing I did with Dan was to walk him through an install of
Debian (wiping the near-useless, corporate Windows image). I wanted
him fully in control of, and responsible for, his own development
environment. I never sat at his keyboard, and all exercises took place
at his computer.
From here I took a bit of an unconventional approach: I decided he was
going to learn from the bottom up, starting with C. There would be no
Fisher-Price-esque graphical programming language (yes, some mentors
actually do this), not even an easier, education-friendly, but
production-ready language like Python. I wanted him to internalize
pointers before trusting him with real work. I showed him how to
invoke gcc, the various types of files involved, how to invoke the
linker, and lent him my hard copy of first edition K&R.
Similarly, I wasn’t going to start him off with some toy text editor.
Like with C, he was going to learn real production tools from the
start. I gave the Emacs run-down and started him on the tutorial
(C-h t). If he changed his mind later after getting more experience,
wanting to use something different, that would be fine.
Once he got the hang of everything so far, I taught him Git and
Magit. Finally we could collaborate.
The first three months were spent on small exercises. He’d learn a
little bit from K&R, describe to me what he learned, and I’d come up
with related exercises, not unlike those on DailyProgrammer, to
cement the concepts. I’d also translate concepts into modern C (e.g.
With K&R complete, he was ready to go beyond simple exercises.
Unfortunately, I wasn’t able to involve him in my own work at the
time. His primary interests included graphics, so we decided on a
multi-threaded, networked multi-processor raytracer.
It was a lot more educational for us both than I expected. I spent a
significant amount of personal time learning graphics well enough to
keep ahead: color spaces, blending, anti-aliasing, brushing up on
linear algebra, optics, lighting models, modeling formats, Blender,
etc. In a few cases I simply learned it from him. It reminds me of a
passage from The Moon is a Harsh Mistress (the namesake of this
I liked Prof. He would teach anything. Wouldn’t matter that he knew
nothing about it; if pupil wanted it, he would smile and set a
price, locate materials, stay a few lessons ahead. Or barely even if
he found it tough—never pretended to know more than he did. Took
algebra from him and by time we reached cubics I corrected his probs
as often as he did mine—but he charged into each lesson gaily.
I started electronics under him, soon was teaching him. So he
stopped charging and we went along together until he dug up an
engineer willing to daylight for extra money—whereupon we both paid
new teacher and Prof tried to stick with me, thumb-fingered and
slow, but happy to be stretching his mind.
Since this was first and foremost an educational project, I decided we
would use no libraries other than the (POSIX) C standard library. He
would know how nearly every aspect of the program worked. The input
(textures) and output formats were Netpbm PPMs, BMP files, and
YUV4MPEG2 (video), each of which is very easy to read and
write. It loaded 3D models in the easy-to-parse Wavefront .obj
format. It also supported a text rendered overlay, initially
using our own font format and later with fonts in the Glyph Bitmap
Distribution Format — again, easy to parse and use. The text
made it possible to produce demo videos without any additional editing
(see the above video).
After a year on the raytracer, he had implemented most of what he
wanted and I had an opportunity to involve him in my funded research.
By this point he was very capable, quickly paying back his entire
Together we made rapid progress — much more than I could alone. I
can’t go into the specifics, but much of his work was built on lessons
learned from the raytracer, including an OpenGL display and
SIMD-optimized physics engine. I also taught him x86 assembly,
which he applied to co-author a paper, ROP Gadget Prevalence and
Survival under Compiler-based Binary Diversification Schemes
To reiterate, an important part of this entire journey was the
influence he had over his own work. He had say on the direction of
each project. Until he started earning a college intern pay
(post-graduation), I had no ability to make him do anything he didn’t
want to do. I could only rely on his motivation. Fortunately what
motivates him is what also motivates me, so to find the framing for
that motivation I only had to imagine myself in his shoes.
An important aspect I hadn’t noticed until the second year was
respect. Most of Dan’s interactions with other co-workers was very
respectful. They listened to what he had to say and treated it with
the same respect as they would a regular, full-time co-worker. I
can’t emphasize how invaluable this is for a student.
I bring this up because there were a handful of interactions that
weren’t so respectful. A few individuals, when discovering his status,
made a jokes (“Hey, where’s my coffee?”) or wouldn’t take his comments
seriously. Please don’t be one of these people.
What’s comes next?
In many ways, Dan is starting college in a stronger position than I
was finishing college. The mentorship was a ton of vocational,
practical experience that doesn’t normally happen in a college course.
However, there’s plenty of computer science theory that I’m not so
great at teaching. For example, he got hands on experience with
practical data structures, but only picked up a shallow understanding
of their analysis (Big O, etc.). College courses will fill those gaps,
and they will be learned more easily with a thorough intuition of
As he moves on, I’ll be starting all over again with a new student.