Background Early and regular developmental screening can improve children's development through early intervention but is insufficiently used. Most developmental problems are readily evident at the 18‐month well‐baby visit. This trial's purpose is to: (1) compare identification rates of developmental problems by GPs/family physicians using four evidence‐based tools with non‐evidence based screening, and (2) ascertain whether the four tools can be completed in 10‐min pre‐visit on a computer. Methods We compared two approaches to early identification via random assignment of 54 families to either: ‘usual care’ (informal judgment including ad‐hoc milestones, n = 25); or (2) ‘Evidence‐based’ care (use of four validated, accurate screening tools, n = 29), including: the Parents' Evaluation of Developmental Status (PEDS), the PEDS‐Developmental Milestones (PEDS‐DM), the Modified Checklist for Autism in Toddlers (M‐CHAT) and PHQ9 (maternal depression). Results In the ‘usual care’ group four (16%) and in the evidence‐based tools group 18 (62%) were identified as having a possible developmental problem. In the evidence‐based tools group three infants were to be recalled at 24 months for language checks (no specialist referrals made). In the ‘usual care’ group four problems were identified: one child was referred for speech therapy, two to return to check language at 24 months and a mother to discuss depression. All forms were completed on‐line within 10 min. Conclusions Despite higher early detection rates in the evidence‐based care group, there were no differences in referral rates between evidence‐based and usual‐care groups. This suggests that clinicians: (1) override evidence‐based screening results with informal judgment; and/or (2) need assistance understanding test results and making referrals. Possible solutions are improve the quality of information obtained from the screening process, improved training of physicians, improved support for individual practices and acceptance by the regional health authority for overall responsibility for screening and creation of a comprehensive network.