Measuring the benefits obtained from the use of executive and organisational coaching is of interest both to coaching service providers and to the organisations who engage their services. Survey instruments, designed to measure coaching effectiveness, have emerged as a means of easy access to information on the success of the coaching provided to individual recipients (termed in this paper 'coaching counterparts'). However, the appropriateness and reliability of the instruments used are critical to good-quality coaching evaluation. This paper argues that reliability tests should be undertaken, and assessments made, in terms of the general efficacy of any instrument that is used. It reports on a study that investigated the reliability of a custom-designed survey instrument, the Coaching Effectiveness Survey (CES) which was developed by the Institute of Executive Coaching and Leadership, a commercial coaching service provider and coach training organisation in Australia. Although the CES has been in use since 2005, this study was completed when a population size of 291 coaching counterparts was reached in 2011. Results revealed that the CES is a reliable survey instrument and that coaching counterparts were most satisfied with the coaching experience for developing benefits in key intrapersonal and interpersonal areas, and, importantly, self-efficacy. Finally, this paper reminds us that although no survey instrument is sufficient for measuring the human experience of coaching (the 'immeasurables'), surveys can be a useful and convenient starting point for investigating coaching effectiveness.