UK visit visa refusal- what evidence do we provide? [closed]

My partner has now been refused four times for a visit visa over the space of 18 months due to varying reasons. I would like to know what evidence people are submitting as ours clearly is not effective enough.

He is a student studying at a vocational college for a year and then has an internship for 6 months- we submitted school receipts to show payment, plus a letter from the school giving details such as start date, when they expect him to return, confirmation of course name, ID number and enrollment. He is supported by me (his British girlfriend who resides and works in the same country as him (Ghana)) as well as savings he has in a joint account with me- at the last visa application there was approximately £4000 in the account. My brother and mother in England agreed to sponsor him and so sent bank slips, passport photocopies, payslips and evidence showing that the house is owned. We also provided tenancy agreements, my contract from my workplace, my residence permit, photos of us (as this was a reason for refusal before) in support of his position.

What other evidence can we provide to show he is a genuine visitor and will leave the UK?