Attitudes towards inclusion (ATI) are regarded as an important aspect for the implementation of inclusive education. Yet, explicit measures of ATI have some limitations. Single-target implicit association tests (ST-IAT) provide an opportunity to an implicit ATI measure based on differences in reaction times. However, this can be a time-consuming procedure. The present study is a replication and extension of the study 'Implicitly measuring attitudes towards inclusive education: a new attitude test based on single-target implicit associations' by investigating reliability of a shortened version of the ST-IAT Inclusion. Prior studies did not investigate the reliability continuously, nor did they consider different ways of calculating the ST-IAT effect size (D-score). In this study, data from 594 university students are analysed to evaluate the reliability of a shortened ST-IAT Inclusion. Results show that the reliability of the shortened ST-IAT is good and in line with findings on reliability of other ST-IAT procedures. However, the difference between several D-score procedures was rather marginal. Altogether, the shortened ST-IAT Inclusion can provide an economic and reliable measure for ATI.