In this single-case study, we evaluated the effects of PESTS, a simple mnemonic strategy to help students remember how to spell difficult words. Our participant was a 9;6-year-old girl with a suspected learning disability in reading and writing. We applied a multiple-baseline design across word sets with one follow-up measurement two weeks after the end of the intervention. The dependent measure was the number of correctly spelled words from a list of 15 difficult nouns. After only a couple of days, the student reached a perfect score on the test and even after two weeks did not commit a single spelling mistake. Although this is only a small single-case study, the findings give reasons for optimism that PESTS can be a very effective tool in supporting students with learning disabilities to overcome their spelling problems.