Students who are having difficulties with opening and closing containers and removing and replacing objects in an assembly line kind of setting would obviously benefit most from practice. Two strategies might be beneficial in improving these skills.
First, students can practice these skills individually and at their own pace before becoming part of an assembly line. This builds confidence as well as speed and accuracy before they are placed in a more competitive structure. (While no one may say so, when students are placed side by side or around a table, they are quite aware of who is and is not the most accurate, who is and who is not the fastest.)
Second, students can begin their assembly line with rather large containers and objects which will, presumably, be easier for them to handle; items can be spaced farther apart so students have more time, as well. When they are ready (as determined by the teacher or by a predetermined number of "practice" rounds), decrease the size of the objects and space them a bit closer together. This can be repeated in as many stages and as many times as needed in order for students to achieve success. Obviously this strategy of moving from larger objects to smaller ones can also be used when students are practicing individually.
While it probably goes without saying, setting a tone of cooperation and encouragement rather than pressure and criticism will also make a dramatic difference in how well students achieve the goal. Setting high expectations is a positive thing when it is coupled with positive reinforcement--something which is true for all of us.