Is on-job training more effective compared to calendar-wise external training? How much difference do they make to organizational growth?

When we talk about comparison between the two i.e. the OJT and Calendar based, i would say it depends upon the skill requirement and the target employees level. If Technical and more detailed and specific learning is required for the employee which need to go through a planned and scheduled learning, feedback and followup chain then the OJT is demanded than calendar based. Calendar Based training programs are short term  like normally3-5 days duration.