Background: Growth is a crucial inconsistent parameter, which is a primary requisite in diagnosing and planning orthodontic and orthopedic treatment. The use of the epiphyseal development of the middle phalanx of the third finger (MP3) radiograph is advisable instead of hand and wrist radiographs for growth assessment. Aim: (1) To propose a simple, precise, and reliable classification system of MP3 staging—RMS MP3 classification and (2) to check the reliability of newly proposed RMS-MP3 classification in assessing the skeletal maturity. Materials and methods: Standardized MP3 digital radiographs of 276 children between 5 years and 13 years of age were included in the study. The epiphysis and diaphysis were measured, and the percentage of epiphysis formed when compared to diaphysis was obtained using our formula. A new classification was designed and proposed. The assessment of the MP3 developmental stages was carried out by all the four investigators (two pedodontists and two nonpedodontists) according to the older classification by Liete et al. and the newly proposed RMS-MP3 classification. Results: Among nonpedodontists, there was 51% perfect agreement of maturity stages according to old classification and 90% perfect agreement according to newly proposed classification. Among pedodontists, there was 90% perfect agreement of maturity stages according to old classification and 99% perfect agreement according to the newly proposed classification. An estimated 89% of agreement was seen in RMS-MP3 classification among all the four observers when compared to 38% of agreement in the old classification. Conclusion: The newly proposed RMS-MP3 classification can be an alternative and perfect aid in assessing growth with accuracy, precision, ease, and an increased reliability.