As software becomes increasingly important to all aspects of industry, there is a need to encourage practitioners to adopt best practice to improve the quality of the processes in use, and therefore achieve targets relating to time, budget and quality. The software development industry is dominated by small firms. The effectiveness of assessment-based software process improvement for small organisations needs to be evaluated. Following an extensive industry survey, a detailed evaluation of a process improvement program including eight key processes was carried out in 22 small firms. The study confirmed that there is wide variation in the extent of adoption of software development best practice. It also showed that small firms can benefit from a low cost process improvement program with a restricted scope, a short time frame to evaluation, and mentoring. The outcomes from this research will be of interest to software developers and managers as it has the potential to better equip practitioners and consultants to undertake software process improvement, hence increasing the success of small software development firms in domestic and global markets.