Background: The purpose of this study was to evaluate the effect of slow, loud, and clear speaking styles on the scaled intelligibility of speakers with dysarthria and neurotypical controls across the course of a reading passage. Methods: 30 speakers with Multiple Sclerosis (MS), 16 with Parkinson’s disease (PD), and 32 control speakers were studied. Speakers read the Hunter Script in habitual, slow, fast, loud, and clear speaking styles. Three fragments near the beginning, middle, and end of the reading passage were extracted, mixed with multitalker babble, and presented to 415 adult online crowdsourced listeners. Listeners judged intelligibility of fragments using a continuous visual analog scale, with the raw score (integer between 0 and 100) as the primary outcome measure of interest. Linear mixed models were used to statistically compare groups, speaking styles, and fragments. Results: Overall, the control group was more intelligible compared to both clinical groups. Scaled intelligibility was not significantly different between the MS and PD group. Pooled over fragments, the control group had lower intelligibility during slow and loud speech compared to habitual speech, whilst intelligibility of clear speech did not differ from habitual speech. Both clinical groups were more intelligible during clear speech compared to habitual speech, whilst intelligibility of slow and loud speech did not differ from habitual speech. Pooled over speaking styles, all groups displayed higher intelligibility for the end fragment compared to the beginning and middle fragments. Intelligibility differences among fragments were not explained by lexical variables. Effects of speaking style on intelligibility over the course of the reading passage differed between speaker groups. Conclusion: Compared to habitual speech, the clear speaking style yielded largest intelligibility gains for both clinical groups (7-9%). Within-task variation for paragraph-level speech materials can play a significant role when evaluating the effectiveness of speaking styles used in the clinical management of dysarthria.