The objective of this study was to determine school student's postural and self-reported responses to realistic daily schoolbag carriage and to provide support for an upper schoolbag weight limit. Sixteen boys carried unloaded, 5%, 10%, 12.5% and 15% of body weight (BW) schoolbag loads, each for a simulated school day. The 10% BW condition was repeated with tightened shoulder straps. Participants' posture was quantified and a questionnaire asked them about a number of areas relating to the physical strain caused by each schoolbag. Posture, rating of perceived exertion (RPE) and muscular strain and ability to walk and balance were significantly affected when student's schoolbag load reached 10% BW. It is suggested that 15% BW may be excessive, which supports a schoolbag weight limit of 10% BW for a typical school day. Posture, RPE and muscular strain and ability to walk and balance were not significantly affected by the duration of carriage or by shoulder strap tightness.