The aim of this study was to determine the effects of pre-season strength training on bilateral and unilateral jump performance and the bilateral deficit (BLD) in Premier League academy soccer players. Fourteen male academy players (age: 16.36 ± 0.50 years; body mass: 73.45 ± 8.43 kg; height: 1.80 ± 0.09 m) performed one upper body and one lower body strength session per week, for eight weeks. Bilateral and unilateral countermovement jumps (CMJ) were assessed pre and post-intervention with jump height, mean force, reactive strength index modified (RSI-Mod) and time to take-off reported for each test. In addition, the BLD was also computed for each metric. Results showed meaningful and significant increases in unilateral jump height on the left (g = 1.00; p = 0.02) and right (g = 0.77; p = 0.039) legs, and for the BLD for jump height (g = 0.67; p = 0.046). No other significant changes in jump performance were evident. Despite numerous non-significant changes in jump performance at the group level, individual analysis showed numerous players exhibited percentage improvements greater than the variance in the test (as depicted by the coefficient of variation), across all metrics. Thus, the results illustrate that a single lower body strength session per week is enough to elicit positive improvements in jump performance for all metrics when assessed on an individual basis, but only for unilateral jump height, when assessed at the group level. Significant increases were also evident for jump height BLD. Despite the majority of players exhibiting improvements in jump performance, some small reductions in performance were also evident. Given the requirement for soccer players to be competent during unilateral movement patterns, an increase in the BLD may be favourable, as it shows greater improvements in unilateral test scores compared to bilateral.