In an observational study, three different treatment schedules with praziquantel were assessed in a Merino land sheep flock from southern Germany. The herd had a known history of severe recurrent Moniezia spp. infections. After turnout to pasture, three hundred lambs between 8 and 14 weeks old were weighed and randomly allocated to three different groups. They were treated with praziquantel (Cestocur®) at a dose of 3.75 mg/kg body weight using the following schedules: group 1 treated four times at monthly intervals (Days 1, 31, 59, 91); group 2 treated three times at six-week intervals (Days 16, 59, 105), group 3 treated twice at an eight-week interval (Days 31, 91). Based on faecal examinations, all lambs were negative for Moniezia spp. on Day 1. At study end (Day 126), higher body weights were seen in group 1 (49.9 ± 5.8 kg; 49.9 kg) than in group 2 (48.7 ± 5.5 kg; 49.0 kg) and in group 3 (47.5 ± 5.4 kg; 47.5 kg) (mean ± SD; median). Overall weight gains were significantly higher in group 1 (22.5 ± 1.8 kg; 22.3 kg) compared to group 2 (20.8 ± 1.4 kg, 21.0 kg; p < 0.0001) and group 3 (19.3 ± 2.2 kg, 19.6 kg; p < 0.0001). The results show that praziquantel treatments applied early in the grazing season and in monthly intervals were more beneficial for body weight developments in lambs than applied at six-weekly or eight-weekly intervals.