I'm not going to sugarcoat it: the HPT caught me completely off guard the first two times. I work in performance consulting and honestly thought my on-the-job experience would carry me through. Wrong. The exam has some really specific domains around human performance technology models — Gilbert's Behavior Engineering Model especially — that you need to know cold, not just have a vague familiarity with.
What finally clicked for me was combining Thomas Gilbert's original text with a structured HPT practice test routine. I did 30-40 questions every morning for six weeks before my third attempt. The practice questions exposed gaps I didn't even know I had — particularly around performance analysis versus cause analysis. I was conflating those constantly.
For anyone prepping right now: don't underestimate the evaluation and measurement domain. It's heavier on the actual exam than any study guide I found suggested. I scored a 78 on my first attempt, a 74 on my second (somehow worse, stress maybe?), and finally passed with an 84. Timeline from starting serious prep to passing was about 10 months total. Happy to answer questions if anyone's in the thick of it.